Kanata optical monitoring of radio galaxy NGC 1275
Kensei Shiki,1 Y. Fukazawa,1 Y. Tanaka,1 R. Itoh,1 2 K. Takaki,1 M. Kawabata,1T. Nakaoka,1 T. Abe,1 N. Kawahara,1 J. Hirochi,11Department of Physical Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526
2

Department of Physics, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8551
E-mail(FS): shiki@astro.hiroshima-u.ac.jp
Abstract

NGC 1275 is a radio galaxy, located at the center of Perseus cluster. The multi-wavelength spectrum
from radio to gamma-ray of NGC 1275 is similar to that of blazars, and it shows a variable gamma-rayactivity. NGC 1275 showed broad emission lines in optical band and a Fe-K line in X-ray band which aresimilar to Seyfert galaxies. Therefore emission of accretion disk dominates in optical and X-ray bands.
In previous works (e.g., Yamazaki et al. 2013), there was no evidence about time variability in the
optical bands from 2010 to 2011, and X-ray bands from 2006 to 2011. On the other hand, Aleksic etal. (2014) showed a variability in gamma-ray and optical bands by the data of MAGIC between October
2009 and February 2010, Fermi-LAT and KVA in between and August 2010 and February 2011. In theirpaper, optical variability was also reported.
Fukazawa et al. 2016 (astro-ph) has reported graduallybrightening of NGC 1275 in X-ray correlated with gamma-ray activity from 2013 to 2014. Based on theseresults, we expect a jet origin brightening in optical band during the same time period. We performed
optical and near-infrared photometry using HONIR installed on the 1.5 m Kanata telescope since February
2015. Furthermore, we analyzed X-ray archival public data of XRT onboard the Swift satellite, and also
investigated time variability correlation between X-ray and optical bands.
Key words: AGN Jet, Radio Galaxy, Kanata Telescope, Swift, Fermi

1. NGC 1275
NGC 1275 is a radio galaxy located at the center of Perseus cluster, and object position is RA =03h:19m:36.21s, Dec = +41:29 :57.9 . As shown inFig. 1, the emission from NGC 1275 has been observedin the broad-band energy range from radio to gammarays. NGC 1275 showed emission lines in optical bandand X-ray band, suggesting that the emission associated with the accretion flow exists. On the other hands,
there are strong variabilities in gamma-ray band. Recently, MAGIC and VERITAS (both of them are Atmospheric Cherenkov Telescope) reported the detectionof very-high-energy gamma-ray activity from NGC 1275
during the same epoch in Oct. 2016. Therefore, the jet
must contribute to the emission of NGC 1275 in the radio and gamma-ray band. But the radiation mechanism
and the structure of jets have not been understood yet.
2. Data Reduction
2.1. Swift satellite and XRTThe Swift is a multi-wavelength observation satellite
launched on November 20, 2004. Swift has three instruments; Burst Alert Telescope (BAT), X-ray Telescope

Fig. 1: The spectral energy distribution of NGC 1275
(S. Yamazaki et al 2013)(XRT), and UV/Optical Telescope (UVOT). The XRT
focuses on X-ray with 23.6 x 23.6 arcmin FOV and 0.2-10
keV energy range.
2.2. X-Ray Data Analysis
We used public data of Swift XRT obtained from July
2007 to November 2016. The bright emission from thePerseus cluster was also observed, and thus we extracted
the XRT spectrum within 0.3 arcmin of NGC 1275, and2.3.

1.2e-06
Fermi 1week bin

FLUX [photn/cm2/s]

performed the spectral analysis of AGN. The background
spectrum was obtained at the position of 60–65 arcsec from NGC 1275, and then subtracted from NGC1275 spectrum. We fitted all the XRT spectra withwabs*pegpwrlw in the XSPEC model.

1.0e-06
8.0e-076.0e-074.0e-072.0e-07

Kanata telescope and HONIR

Swift XRT

5.0e-11
4.5e-11
4.0e-113.5e-113.0e-112.5e-112.0e-111.5e-111.0e-11
54000

55500

56000

56500

57000

57500

58000

[photn/cm2/s]

2.0e-06
Fermi 1day bin
Fermi 1week bin
1.0e-06

6.0e-11year
2015
2016

V
42150

R
36141

J
42151

Ks
36141

normed mag

0.2

RV

00.4

normed mag

Table 1: Kanata Telescope photometry data list

Swift XRT

4.0e-11

0.4

J

0.2
057300Results Of X-ray And Optical Data

Fig. 2 shows light curves, based on all Fermi achival
gamma-ray data and Swift X-ray data. There are strong
variabilities in gamma-ray band. We can see significant
brightness increase around MJD 5550 and 57000 in both
gamma-ray and X-ray. Fig. 3 shows multi-wavelength
light-curve from 57300 to 57800. In s short time-scale,no obvious synchronized feature among the bands can beseen.

4.

55000

Optical observation and Analysis

We took data on 45 nights in February 2015 - November 2016. Optical data were obtained in the V and R
bands, and NIR data in the J bands. The host galaxyand extended nebula are very bright, and thus it is hardto subtract the emission from these components. Table
1 shows the number of data obtained with HONIR.

3.

54500

Fig. 2: Fermi and Swift whole period light-curve[erg/cm2/s]

2.4.

FLUX [erg/cm2/s]

5.5e-11

Kanata is 1.5m Ritchy-Cretien telescope at HigashiHiroshima Observatory. It has 1 Cassegrainfocus and 2
Nasmythfocuses. Hiroshima Optical and Near-Infrared
camera (HONIR), installed on the Cassegrainfocus, cantake image in the optical and near-infrared (NIR) band
simultaneously. Observed targets are focused especiallyon variable objects such as blazars, supernovae, andgamma-ray bursts.

Summary and Feature work

In this work, we analyzed X-ray data of Swift-XRT and
optical and NIR data of HONIR. We compared these results with gamma-ray archive light curve of Fermi-LAT.
Currently we do not see a significant correlation between
optical and Gamma-ray for the short-term gamma-rayvariability. Because the optical flux estimation is still
not optimized in this work, we are improving the opticalflux estimation.

57400

57500
57600
TIME [MJD]

57700

57800

Fig. 3: Multi-wavelength light-curve from 57300 to57800[MJD]. From the top of figure, Fermi gamma-ray,
Swift X-ray, Kanata optical and Kanata near infrared.
5. References
References
Aleksic, J., et al. March 6, 2014, A-2013-22951 arxiv
Yamazaki, S., et al. ”X-Ray and Optical Monitoring of a
Gamma-Ray-Emitting Radio Galaxy,NGC 1275” 25April 2013
Fukazawa, Y., et al. ”X-ray variability of GeV gammaray emitting radio galaxy NGC 1275” 12 August 2016
The Astronomer’s Telegram #9689
The Astronomer’s Telegram #9690